BlueBelle I don't know much about trans people and I don't know much about children, so maybe I've got this all wrong, but this is my interpretation.
The doll is a plastic figure made to represent Laverne Cox. Cox is an actress who happens to be trans. The doll kinda looks like Laverne, but Barbie doesn't have visible sexual organs. When they brought out the Rosa Parks doll, or the Sarah Gilbert doll, there was nobody complaining that it was a travesty, that the dolls couldn't represent those women. Nobody is complaining that the Ken doll is a waste of time because it doesn't have the male bits on show.
The doll is just showing that whoever you are you can be a Barbie. Whether you are a civil rights activist, a vaccine researcher or if you were born a man and appear in Television dramas.
But some are jumping in the trans bit, starting threads that get people all indignant, or suggesting that it's the sexualisation of children. It's just a doll representing someone who was born a man. That's all.